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Heat-sealable isomeric co-polyimide (CPI) films with enhanced atomic oxygen (AO) resistance and mechanical strength were synthesized from 2,3,3′,4′-oxydiphthalic anhydride (aODPA), 4,4′-oxydianiline (ODA), and 2,5-bis [(4-aminophenoxy)phenyl]diphenylphosphine oxide (BADPO). We investigated how the molecular structure and diamine ratio affected the thermal properties, solubility, mechanical properties, AO resistance and heat-sealability. The diphenylphosphine oxide (DPO) side group decreased the CPI film mechanical strength and its higher ODA reactivity increased the molecular weight. At 10 mol% ODA in the aODPA-BADPO system, the CPI film exhibited increased tensile strength with no detriment to the AO resistance. Meanwhile, the CPI films demonstrated good heat-sealability indicated by a completely merged interface after heat sealing. [ABSTRACT FROM AUTHOR]

Aromatic polyimides have excellent thermal stability, mechanical strength and toughness, high electric insulating properties, low dielectric constants and dissipation factors, and high radiation and wear resistance, among other properties, and can be processed into a variety of materials, including films, fibers, carbon fiber composites, engineering plastics, foams, porous membranes, coatings, etc. Aromatic polyimide materials have found widespread use in a variety of high-tech domains, including electric insulating, microelectronics and optoelectronics, aerospace and aviation industries, and so on, due to their superior combination characteristics and variable processability. In recent years, there have been many publications on aromatic polyimide materials, including several books available to readers. In this review, the representative progress in aromatic polyimide films for electronic applications, especially in our laboratory, will be described. [ABSTRACT FROM AUTHOR]

Intrinsically heat-sealable polyimides with atomic oxygen (AO) resistance (ARPIs) were synthesized from 2,3,3′,4′-oxydiphthalic anhydride (aODPA), 2,5-bis[(4-aminophenoxy)phenyl]diphenylphosphine oxide (BADPO), and para -phenylenediamine (PDA). The effects of the molecular structure and diamine ratio were investigated on the properties of the ARPI, including mechanical property, thermal property, heat sealability, and AO resistance. Heat sealability and AO resistance were realized for the ARPI film by combining the asymmetry of the aODPA moiety and the passivated layer forming characteristic of diphenylphosphine phosphine oxide group. Meanwhile, the deficiency of low mechanical strength and thermal resistance, commonly existing in a completely BADPO-derived polyimide system, was remedied effectively by the higher reactivity and rigidity of PDA. [ABSTRACT FROM AUTHOR]

ABSTRACT To investigate the effect of reactive end-capping groups on film-forming quality and processability, a series of molecular weight-controlled aromatic poly(amic acid) (PAA) resins functionalized with phenylethynyl end groups were prepared via the polycondensation of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), para-phenylenediamine (PDA), and 4-phenylethynyl phthalic anhydride (PEPA) served as molecular-weight-controlling and reactive end capping agent. The PAA resins with relatively high concentrations endow enhanced wetting/spreading ability to form PAA gel films by solution-cast method which were thermally converted to the fully-cured polyimide (PI) films. The mechanical and thermal properties of PI films were investigated as a function of PAA molecular weights ( Mn) and thermal-curing parameters. Mechanical property, dimensional stability and heat resistance of the fully-cured PI films with PAA Mn > 20 ×103 g mol−1 are found to be better than that of their unreactive phthalic end-capped counterparts. The covalent incorporation of chain-extension structures in the backbones, induced by thermal curing of phenylethynyl groups, might facilitate yielding a higher degree of polymer chain order and consequently improved resistance strength and elongation at break to tensile plastic deformation. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45168. [ABSTRACT FROM AUTHOR]

A novel fluorinated ester-bridged aromatic diamine, bis(2-trifluoromethyl-4-aminophenyl)terephthalate (CF3-BPTP) was synthesized, which was employed to prepare a series of fluorinated ester-bridged polyimide (PFEI) films with controlled ester-bridged segments and fluorine contents in the polymer backbone. The PFEI films were prepared by copolymerization of biphenyl tetracarboxylic dianhydride as aromatic dianhydride monomer and the aromatic diamine monomer mixture consisting of p-phenylenediamine and different amounts of CF3-BPTP. Experimental results indicated that the films’ water uptakes (Wus) reduced with increasing of the CF3 groups loadings in the ester-bridged polyimide backbones while keeping the films with low enough coefficient of thermal expansion (CTE). By controlling CF3 group loadings, polyimide films with desirable combination of thermal, mechanical, and dielectric properties for application in high density and thinner flexible printed circuits (FPCs) have been obtained. Thus, polyimide films with CTE of ≤20 × 10−6 1/K (ppm/K) at 50–200°C, glass transition temperature of ≥310°C, Young’s modulus of ≥6.0 GPa, Wu of as low as 0.7 wt%, dielectric constant (ε) of 3.3 have been obtained. The two-layer flexible copper clad laminate prepared by coating the polyimide precursor resin poly(amid acid) solution on the surface of copper foil followed by thermal imidization at elevated temperature did not show apparent curling due to its closed CTE value. [ABSTRACT FROM AUTHOR]

Abstract: A novel meta-substituted aromatic diamine containing trifluoromethyl and sulfonyl groups in the backbone, i.e., 2,2′-bis[4-(3-amino-5-trifluoromethylphenoxy)phenyl]sulfone (m-6FBAPS), was synthesized and characterized. A series of semi-aromatic polyimides were prepared from 1,2,4,5-cyclohexanetetracarboxylic dianhydride (CHDA) and various aromatic diamines. These polymers exhibited excellent solubility, high thermal stabilities and good mechanical properties. All semi-aromatic polyimide films showed considerably improved optical transparency as comparing with traditional aromatic ones due to the incorporation of alicyclic moieties. They gave the UV cutoff wavelengths of 292–314 nm, transmittance at 450 nm > 91% and yellowness indices <3.8. The extremely transparent and entirely colorless films were obtained from the polymers incorporated with bulky electron-withdrawing trifluoromethyl and sulfonyl groups in diamine moieties, such as PI-2, PI-5 and PI-6. Their excellent optical properties are attributed to the distorted molecular conformation combined with the weakened electron-accepting and electron-donating properties of dianydride and diamines, which significantly restrained the formation of inter-/intra-molecular charge transfer interactions. [Copyright &y& Elsevier]

Carborane-containing aromatic polyimide (CPI) films with ultrahigh thermo-oxidative stability at 700 °C have been prepared by casting poly(amic acid) (PAA) resin solution on a glass surface, followed by thermal imidization at elevated temperatures. The PAA solution was prepared by copolymerization of an aromatic dianhydride and an aromatic diamine mixture, including carborane-containing aromatic diamine in an aprotic solvent. The CPI films showed excellent thermo-oxidative stability at 700 °C due to the multilayered protection layers formed on the film surface by thermal conversion of the carborane group into boron oxides. The boron oxide layer enhanced the degradation activation energy and suppressed the direct contact of inner polymer materials with oxygen molecules in a high-temperature environment, acting as a "self-healing" skin layer on the polyimide materials. The CPI-50 film was still flexible and maintained 50% retention of mechanical strength even after thermo-oxidative aging at 700 °C/5 min. The mechanism of thermo-oxidative degradation was proposed. [ABSTRACT FROM AUTHOR]

• Carborane nanocage structure was used for modification of AO resistance. • Carborane-containing PI nanocomposite films achieved both high thermal stability and AO resistance. • More denser passivation layer formed, eliminating the volume shrinkage phenomenon prevalent in POSS-PI films. • The mechanism of "self-healing" characteristic of PI nanocomposite films during AO irradiation was proposed. High-temperature durable polymer films with long-term atomic oxygen (AO) resistant capabilities are highly desired for the development of spacecraft with long-servicing lifetimes in low earth orbit (LEO). The relatively poor AO resistance of conventional polyimide (Kapton® H) film severely limited its applications in LEO spacecraft. In this work, carborane nanocage rich in boron element was introduced into polyimide molecular chain to prolong the atomic oxygen resistance life of polyimide film. A series of carborane-containing polyimide (CBPI) nanocomposite films with ultrahigh AO resistance have been prepared by casting precursor polyamic acid (PAA) solution on a glass plate, followed by thermal imidization at several elevated temperatures. The AO exposure experiments were tested in a ground-based AO effects simulation facility in our laboratory with the filament discharge and bound of magnetic field. Incorporation of carborane nanocage structure apparently improved the thermal stability and AO resistance of the PI nanocomposite films. The CBPI-50 film exhibited the lowest AO average erosion yield (E s) of 2.3 × 10−25 cm3·atom−1 under AO exposure with a fluence of 3.33 × 1020 atoms·cm−2, which is more than one order of magnitude lower than the reference Kapton® H film. The protective mechanism of CBPI nanocomposite films during AO exposure was proposed. [ABSTRACT FROM AUTHOR]

Understanding of the nature of the transition mechanism in UV-visible absorption spectrum may contribute to the designing of highly transparent polyimide (PI) materials. In the present work, structure effect (alicyclic ring, flexible -O- linkage, and -CF 3 ) on the intra- and inter- molecular transition mechanism of optical absorptions in PI model molecules is investigated by the Density functional theory (DFT) in combination with the time dependent DFT calculations. Six pyromelliticdianhydride (PMDA) derived aromatic and six 1,2,4,5-cyclohexanetetracarboxylic dianhydride (CHDA) derived semi-aromatic polyimide (PI) species are considered and their intermolecular transitions are analyzed by designing typical dimers with classical face-to-face π-π stacking orientation. The natural bond orbital method (NBO) is employed to analyze the delocalization degree in the PI species. By calculating the energies of the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) as well as the transition characters between them, the electron excitation nature concerning on the structural variations in the monomers and the dimers are clarified. These theoretical results agree well with the related experimental observations and provide a deep understanding into the transition mechanism of optical absorptions in the PI species. [ABSTRACT FROM AUTHOR]

The thermal imidization process of 1,2,4,5-benzenetetracaboxylic (PMDA)/4,4’-diamnodiphenyl ether (4,4′-ODA) solutions in N -methyl-2-pyrrolidone (NMP) from polyimide (PI) precursor, poly (amic acid) (PAA), was systematically investigated through a series of characterization methods, such as Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). At the low-temperature drying stage, mechanical properties and T g of polymer films were increased as a result of solvent removal. TGA method was used to quantitatively monitor the evaporations of hydrogen-bonded solvents on PAA and of the dehydration during the imidization reaction that occurred above 150 °C. During the imidization stage, the interplay between the solvent evaporation and the imidization was the key factor that determined the enhancement of the mechanical properties and T g . The degree of imidization approached 94% when the temperature was increased to 250 °C. A “complete” imidization was achieved by annealing between 350 and 400 °C. The enhancement in the mechanical properties of final PI films may result from the increased T g and the crystallized structure formed during the annealing stage. [ABSTRACT FROM AUTHOR]